bug#80118: Don't just say "invalid date"

On 2026-01-02 21:59, Dan Jacobson wrote:
> also consider dealing with ET.

Good luck with that. Is that eastern Australia time, eastern European 
time, eastern North America time, 
Ecuador/Egypt/Eritrea/Estonia/Eswatini/Ethiopia Time, East Timor, or 
something else? For what it's worth, POSIX does not allow "ET"; time 
zone abbreviations must be at least 3 characters. Also, real-world 
abbreviations are ambiguous, such as "IST" simultaneously standing for 
time in India, Ireland, and Israel.

> $ date -d '01/30/2026 02:00 PM ET'
> date: invalid date ‘01/30/2026 02:00 PM ET’
> 
> Don't just say "invalid date". Say "invalid date: weird time zone".

Yes, it'd be nice if the date parser pointed out exactly what it didn't 
like.